To improve efficiency and reduce environmental pollution in urban areas, vehicles powered by electricity have been made commercially available and are increasing in popularity. Efficiency of electric powered vehicles such as automobiles, trucks, and railroad vehicles is improved over fossil fuel-powered vehicles since no power is consumed when the vehicle is not in motion and some of the power consumed during acceleration or hill-climbing can be recovered by using the electric motor of the vehicle as a generator during braking and coasting even though the weight of batteries and electrical controls for the motor is a significant contribution to the overall weight of the vehicle.
For that reason and to avoid the additional weight of strengthening structure to support very large batteries, battery power storage capacity and, consequently, the range of the vehicle is compromised and there is a need to frequently re-charge the batteries in electric-powered vehicles. When re-charging is performed, electrical power is generally provided from the so-called power distribution grid or a generator operating from so-called renewable resources such as solar panel and wind farms that also supply power with alternating current (AC), for efficiency of transmission, to other loads. Therefore, battery chargers and many other devices are required to include power factor correction (PFC) circuits and filters in order to avoid reflecting noise back to the power source or distribution system and devices connected to it.
A PFC circuit seeks to control transfer of power from an AC source such that the current drawn by a load is aligned in phase with the AC voltage for efficiency of power transfer. This is usually accomplished for loads operating on direct current (DC) power by rectifying the AC input voltage and using a converter including one or more pulse width modulated switches or other switching control arrangement to regulate the current drawn from the source to match the phase of the input voltage. A boost converter is usually the converter topology of choice for charging batteries for electric-powered vehicles since the DC voltage required is substantially higher than the peak of the AC voltage available.
Boost converters operate by switching power from a rectifier connected to a power source through an inductor such that the volt-second balance of the voltage developed across the inductor increases the peak voltage at the inductor output. This periodic high voltage must then be filtered because the product of sinusoidal voltage and current variation inherently produces a large low frequency, second-order (e.g. second harmonic of the AC frequency) power ripple which has required a very large-valued filter capacitor to achieve adequate regulation since a fluctuating voltage is not efficient for charging of batteries and may, over time, compromise the power storage capacity of the batteries. Therefore, a large filter capacitor has generally been required to store the power in the low frequency ripple.
The entire battery charging apparatus must be designed for a particular vehicle or vehicle model since electric powered vehicles have different power requirements, different power storage capacities and operate at different voltages but must be capable of receiving power from a standardized power source such as the power distribution grid. Therefore, a filter capacitor capable of storing the power in the power ripple during battery charging must be of significant volume and weight and must be carried in the vehicle. Thus, the size and weight of the filter capacitor (sometimes referred to as a DC-bus capacitor) may compromise operation of the vehicle by occupying space, reducing vehicle payload space, and causing consumption of some level of power (e.g. to accelerate its weight) but is not involved in actual operation of the vehicle but only used during battery charging while the vehicle is stationary.